This Invention relates generally to a drive-on dry dock and, more particularly, to a drive-on dry dock which is especially suited for a boat longer than about thirty feet and weighing more than about seven thousand pounds.
A drive-on dry dock is used to store a boat out of the water to minimize problems of corrosion, marine growth, and leakage. Of particular relevance to the present invention is a drive-on dry dock for larger-sized watercraft, such as a boat which is longer than about thirty feet and weighs more than about seven thousand pounds. In designing a drive-on dock for such a craft a number of factors must be taken into consideration. First, its center of gravity is usually substantially rearward of the geometrical center of the craft. In addition, care must be taken to assure that the motors"" cooling water inlets are kept submerged during the drive-on procedure.
In the past, dry docks for the boats of this size have included a rigid framework including hull-supporting bunks and inflatable pontoons which lift the framework between a first position and a second position. In the first position, the framework is submerged so that the boat can be driven over it while afloat. The framework is then moved to the second position where it is substantially horizontal and above the mean water level so that the boat is lifted out of the water. Inflatable tanks have been used to provide the necessary lift, and the rigid framework is kept approximately horizontal by a linkage mechanism between the framework and a supporting frame such as a dock. In these systems the boat""s motors are not normally running during the lifting procedure. The mechanical linkage assures that the boat is lifted horizontally even though its weight is concentrated in the rear.
The present invention provides a drive-on dry dock for large sized craft, e.g., longer than about thirty feet and weighing more than about seven thousand pounds, and a method of dry-docking such a craft.
More particularly, the present invention provides a drive-on dry dock comprising a partially submersible platform, guide surfaces on the platform to position a boat or a watercraft on the dock, and a lift to elevate the submerged part of the dock on command. The platform includes an aft section and a forward section that are transversely hinged together. The guide surfaces define a path for movement of the boat from the aft section of the dock to a rest position in which the boat""s bow engages and is supported by the forward section of the dock. The lift shifts the platform between a first state and a second state. In the first state, the top surface of the forward section of the dock is generally planar and mostly above the mean water level, and the aft section may also have its top surface above the water. In the first state, the aft section is only slightly more than neutrally buoyant and it can easily be pressed downward by the bow of an approaching boat which then may be driven along the path to its rest position. In the second state, the top surface of the aft section is above the mean water level and the craft is out of the water. The hinging between the aft section and the forward section can be accomplished by including a hinge section in the platform between the forward and aft sections of the dock.
The platform can be formed from a plurality of dock units assembled together to form the aft section, the forward section, and the hinge section. The dock units include buoyant units and non-buoyant units, with at least some of the non-buoyant units being positioned in the aft section. The buoyant units have a sealed, air-filled body, and the non-buoyant units have a similar body with openings so that they can fill with water. Selective use of buoyant and non-buoyant units makes it possible to achieve any desired buoyancy in any of the dock sections. When making the platform, a plurality of buoyant units can be assembled together, and then the bodies of selected units may be perforated as required to convert them to non-buoyant dock units.
The dock units are laid out in a rectangular array formed from a series of transverse rows of buoyant units. The length of each row (and hence the width of the resulting dock) is determined by the particular boat for which it is intended, as is the number of rows (and hence the length of the dock). The units are connected to each other by flexible joints which allow the various units to bend or hinge to various degrees with respect to their immediate neighbors as described in U.S. Pat. No. 5,529,013. Overall, the units are arranged so that the forward section remains generally flat and with its top above water, the hinge section can flex, curving downward from the plane of the top of the forward section. The aft section is made rigid by the lift means. The dock is constructed so that in a first state (with the lift means providing no lift) the aft section is only slightly more than neutrally buoyant. In a second state (with the lift means providing lift). The aft section has sufficient buoyancy to support the boat completely out of the water.
At this point, for ease of description, it may be helpful to establish terminology for use in this application. xe2x80x9cLongitudinalxe2x80x9d means parallel to the long direction of the dock, e.g., from fore to aft. xe2x80x9cTransversexe2x80x9d means from side to side, e.g., from starboard to port. Bending is described using the same words. Bending is xe2x80x9ctransversexe2x80x9d when the port and/or starboard edges are higher and/or lower than the center with the result that traversing the dock along a transverse line follows a curve, while traversing the dock along a longitudinal path traces a straight line. Similarly, bending is longitudinal when the aft or fore end of the dock is raised and traversing the dock longitudinally traces a curve while traversing it along any transverse path traces a straight line.
It is desirable to limit transverse flexing of the dock. This keeps the flexible joints between any two rows coaxial and so promotes the desirable longitudinal flexing. To this end transverse beam structures are mounted in the seams between some of the transverse rows of dock units. The preferred beam structure is non-buoyant and includes a beam (e.g., an inverted T-beam) having a web extending into one of the transverse seams. Other beams can be attached to the inverted T-beam and these other beams can be used to mount the lift components (e.g., to form cradles for pontoons). A transverse beam structure can be positioned at each end of the hinge section and a plurality of transverse beam structures can be positioned intermittently throughout the aft section.
The lift for the dry dock can comprise a pair of inflatable devices, particularly pontoons, positioned below and on either side of the path defined by the guide surfaces. The pontoons each have an air tight inner wall which can be selectively connected to a source of air under pressure or vented to the atmosphere, and a corrugated outer wall surrounding the inner wall.
These and other features of the invention are more fully described and particularly pointed out in the claims. The following description and annexed drawings set forth in detail certain illustrative embodiments of the invention, these embodiments being indicative of but a few of the various ways in which the principles of the invention may be employed.